Tuning fork-type vibrating reed, tuning fork-type vibrator and manufacturing method therefor

ABSTRACT

When a thick frequency adjustment metal film of a tuning fork-type vibration piece is irradiated with a beam on a wafer for frequency coarse adjustment, projections are possibly formed on a roughened end of the frequency adjustment metal film. Such projections are pressurized and pushed down not to chip off under any impact, so that the risk of frequency fluctuations is suppressed.

REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 16/467,272 filed Jun. 6,2019, now allowed, which is a 371 of International Patent ApplicationNo. PCT/JP2017/039577, filed Nov. 1, 2017, which in turn claims priorityof Japanese Patent Application No. 2016-249756, filed Dec. 22, 2016. Thesubject matter of the aforementioned prior applications is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a tuning fork-type vibrator used as aclock source for electronic devices and a manufacturing method for thetuning fork-type vibrator, and a tuning fork-type vibration piece thatconstitutes the tuning fork-type vibrator.

BACKGROUND ART

Patent Document 1 describes a manufacturing method for a tuningfork-type vibration piece that constitutes a tuning fork-type vibrator.In this method, outer shapes of multiple tuning fork-type vibrationpieces are formed on, for example, a crystal wafer by photolithographyand etching. The tuning fork-type vibration pieces each have a pluralityof arm portions. An electrode film and a metal film are formed on thesurface of each vibration piece. The metal film is a weight member forfrequency adjustment and is formed on one end side of the arm portions.The metal film is irradiated with a laser beam on the crystal wafer andthereby trimmed for coarse adjustment of frequencies of the respectivevibration pieces.

CITATION LIST Patent Documents

-   Patent Document 1: Japanese Patent Publication No. 2003-133879

SUMMARY OF THE INVENTION Technical Problems

The tuning fork-type vibrator is embedded, together with an oscillatorcircuit, in an electronic device as a clock source. Advancingminiaturization of the electronic devices in recent years is demandingsmaller tuning fork-type vibrators as small in outer dimension as, forexample, 1.6 mm×1.0 mm or less in plan view. This is raising the demandfor correspondingly smaller tuning fork-type vibration pieces.

The manufacture of such miniaturized tuning fork-type vibration piecesrequires a high machining accuracy. The machining accuracy, however, canonly be improved to a limited extent, frequencies of the multiple tuningfork-type vibration pieces formed on the wafer may be inevitably morelikely to fluctuate as the vibration pieces are further miniaturized. Inorder to allow such variable frequencies to stay within a requiredfrequency range, the extent of adjustment may have to be increased whenthe frequencies are coarsely adjusted through the laser irradiation.

Due to the fact that the frequency adjustment metal film is formed in avery limited area of the microminiaturized tuning fork-type vibrationpiece, the metal film may need to be increased in thickness in order toincrease the extent of frequency adjustment through the laserirradiation. To be specific, it may be necessary to form the frequencyadjustment metal film in a thickness of, for example, 3 μm or more usinga technique such as plating.

The multiple tuning fork-type vibration pieces, after their frequenciesare adjusted by irradiating such thicker frequency adjustment metalfilms with a laser beam, are broken off the wafer into individual piecesand are respectively housed in a package to be each supplied as a finalproduct; tuning fork-type vibrator.

In such a miniaturized tuning fork-type vibrator that isfrequency-adjusted by irradiating the thick metal film with a laserbeam, frequency fluctuations may occur under any impact from outside.The frequency adjustment metal film, when partly removed under the laserirradiation, may be roughened with projections at its one end partlyremoved. In case these projections chip off under an external impact,the frequency adjustment metal film may unexpectedly reduce in mass,leading to the frequency fluctuations.

The present invention was accomplished to address the unsolved issue ofthe known art, and is directed to providing a tuning fork-type vibratorthat may excel in impact resistance and accordingly suppress the risk offrequency fluctuations.

Solution to Problem

To this end, the present invention provides the following technicalaspects.

A manufacturing method for a tuning fork-type vibrator is provided. Inthis method, a tuning fork-type vibration piece including a stem portionand a plurality of arm portions extending from the stem portion isjoined to and mounted in a package having a housing portion. This methodincludes a first step of forming a frequency adjustment metal film in atip-side part in a respective one of the arm portions of the tuningfork-type vibration piece, a second step of performing a frequencyadjustment by removing the frequency adjustment metal film in partthrough irradiation of the tuning fork-type vibration piece with a beam,and a third step of applying a load to and pressurizing the frequencyadjustment metal film partly removed.

The second step performs irradiates the tuning fork-type vibration piecewith the beam to partly remove the frequency adjustment metal film forfrequency adjustment. After the frequency adjustment metal film ispartly removed through the beam irradiation, one end partly removed ofthe frequency adjustment metal film may be roughened with projections(hereinafter, “projections”). Any impact from outside large enough tocause the projections to chip off may lead to the undesired event;frequency fluctuations.

In the tuning fork-type vibrator manufacturing method according to thepresent invention, the frequency adjustment metal film is partly removedthrough the beam irradiation in the second step, and the frequencyadjustment metal film is pressurized under the load applied in the thirdstep. In this manner, the projections resulting from the beamirradiation may be pushed down toward the frequency adjustment metalfilm. This may prevent that any external impact damage and chip off theprojections, suppressing the risk of frequency fluctuations.

Preferably, in the second step, the frequency adjustment metal film ispartly removed from the tip-side part toward the stem portion in arespective one of the arm portions, and, in the third step, at least oneend partly removed of the frequency adjustment metal film is pressurizedunder the load applied.

The projections may be generated at one end partly removed of thefrequency adjustment metal film through irradiation of the tuningfork-type vibration piece with the beam. According to the method thusfurther characterized, therefore, the projections may be efficientlypushed down by pressurizing at least the partly removed one end underthe applied load.

Preferably, in the first step, the frequency adjustment metal film isformed in the tip-side part on one of front and back main surfaces in arespective one of the arm portions of the tuning fork-type vibrationpiece, and, in the second step, the frequency adjustment metal film ispartly removed by irradiating the tuning fork-type vibration piece withthe beam directed from another one of the front and back main surfaces.

According to the method thus further characterized, radiation of thebeam is directed downward, from one of the main surfaces of the tuningfork-type vibration piece, toward the other main surface where thefrequency adjustment metal film is formed. Thus, metal fragments chippedoff the frequency adjustment metal film and flying downward may beprevented from adhering again to the tuning fork-type vibration piece.

In the third step, preferably a tool that holds the tuning fork-typevibration piece is used to apply the load to and pressurize thefrequency adjustment metal film when the frequency adjustment metal filmis joined to and mounted in the package.

In the method thus further characterized, the tuning fork-type vibrationpiece may be mounted in the package, and the projections at one end ofthe frequency adjustment metal film resulting from the beam irradiationmay be pushed down well by using such a tool.

When the frequency adjustment metal film is pressurized under the loadapplied with this tool that holds the tuning fork-type vibration piece,a surface of the tool on which the vibration piece is being held maypreferably be pressed against one longitudinal end of the tuningfork-type vibration piece and the frequency adjustment metal film atanother longitudinal end of the tuning fork-type vibration piece.

According to the method thus further characterized, the surface of thetool is pressed against one longitudinal end of the tuning fork-typevibration piece and the thick frequency adjustment metal film at anotherlongitudinal end of the tuning fork-type vibration piece. On the otherhand, the arm portions between these longitudinal ends may be distancedfrom the surface of the tool. This may avoid contact between the tooland electrodes formed on the arm portions and accordingly preventpossible damage to the electrodes.

Preferably, in the third step, at least one of heat and ultrasonic waveis further applied to the frequency adjustment metal film in addition tothe load applied to pressurize the frequency adjustment metal film.

According to the method thus further characterized, heat or ultrasonicwave, as well as the load, is applied to and pressurize the frequencyadjustment metal film. The projections formed at one end of thefrequency adjustment metal film by the beam irradiation, therefore, maybe more reliably pushed down as flat as possible.

Preferably, the frequency adjustment metal film has a thickness greaterthan or equal to 3 μm.

The frequency adjustment metal film thus as thick as 3 μm or more mayallow a large extent of frequency adjustment even for miniaturizedtuning fork-type vibration pieces. In the frequency adjustment metalfilm thus thick, the projections formed at its one end by the beamirradiation may be greater in height and more likely to chip off underan external impact. By pushing down such large projections as flat aspossible, effects of suppressing the risk of frequency fluctuations inthe vibration piece may be even more notable.

A tuning fork-type vibration piece according to the present inventionincludes a stem portion and a plurality of arm portions extending fromthe stem portion. The arm portions each include, in a tip-side part, afrequency adjustment metal film that has been partly removed. Athickness between a raw surface of the tuning fork-type vibration pieceand a surface of the frequency adjustment metal film formed on arespective one of the arm portions at one end partly removed of thefrequency adjustment metal film is greater than a thickness between theraw surface of the tuning fork-type vibration piece and the surface ofthe frequency adjustment metal film in a part of the frequencyadjustment metal film other than the one end. A difference between thethicknesses at the one end and in the part other than the one end isless than or equal to 0.5 times of the thickness in the part other thanthe one end.

After the frequency adjustment metal film is partly removed byirradiating the tuning fork-type vibration piece with the beam, the oneend partly removed of the frequency adjustment metal film may beroughened with projections. The projections thus formed may easily chipoff, causing the undesired event; frequency fluctuations. Theseprojections may easily chip off because of their lengths of more than0.5 times of the thickness between the raw surface of the tuningfork-type vibration piece and the surface of the frequency adjustmentmetal film on a beam-unirradiated part other than the one end.

In the tuning fork-type vibration piece according to the presentinvention, a difference between the following thicknesses; thicknessbetween the raw surface of the tuning fork-type vibration piece and thesurface of the frequency adjustment metal film at the one end partlyremoved of the frequency adjustment metal film, and thickness betweenthe raw surface of the tuning fork-type vibration piece and the surfaceof the frequency adjustment metal film on a part other than the one end,i.e., a difference equivalent to the height of the projections, is lessthan or equal to 0.5 times of the thickness between the raw surface ofthe vibration piece and the surface of the frequency adjustment metalfilm in any beam-unirradiated part other than the one end.

This may be rephrased that, in the tuning fork-type vibration pieceaccording to the present invention, there is no projection greater inheight than 0.5 times of the thickness between the raw surface of thetuning fork-type vibration piece and the surface of the frequencyadjustment metal film in a part other than the one end partly removed ofthe frequency adjustment metal film. This may prevent that theprojections chip off under an external impact, effectively suppressingthe risk of frequency fluctuations.

A tuning fork-type vibrator according to the present invention includesthe tuning fork-type vibration piece according to the present invention,a package body having a housing portion for the tuning fork-typevibration piece to be housed, and a lid member that seals an opening ofthe package body in which the tuning fork-type vibration piece ishoused, wherein the tuning fork-type vibration piece is joined to andsupported by electrodes in the housing portion of the package body.

The tuning fork-type vibrator according to the present invention ismounted with the tuning fork-type vibration piece in which theprojections have been pushed down and substantially flattened. In thistuning fork-type vibrator, the projections may be prevented fromchipping off under an external impact, and the risk of frequencyfluctuations may be accordingly suppressed.

Effects of the Invention

The present invention may avoid the formation of such projections thatstick out from roughened one end of the frequency adjustment metal filmpartly removed, and may accordingly eliminate the risk of the undesiredevent; chipped-off projections under any impact. The tuning fork-typevibrator according to the present invention, therefore, may successfullysuppress the risk of frequency fluctuations and may excel in impactresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view in cross section of a crystal vibratoraccording to an embodiment of the present invention.

FIG. 2 is a plan view of the crystal vibrator illustrated in FIG. 1 fromwhich a lid member has been detached.

FIG. 3 is an enlarged view of a main-surface side of a crystal vibrationpiece illustrated in FIG. 1 .

FIG. 4 is an enlarged view of another main-surface side of the crystalvibration piece illustrated in FIG. 1 .

FIG. 5 is a drawing that illustrates coarse frequency adjustment throughirradiation of a crystal vibration piece with a laser beam.

FIG. 6 is a drawing of a state subsequent to the laser beam irradiationperformed as illustrated in FIG. 5 .

FIG. 7 is a drawing of the crystal vibration piece being mounted on abase with a suctioning tool.

FIG. 8 is an enlarged view in part of the illustration of FIG. 7 .

FIG. 9 is a drawing of a frequency adjustment metal film and itsvicinity in the crystal vibration piece mounted on the base with thesuctioning tool.

FIG. 10 is a graph showing a drop test result of the tuning fork-typevibrator according to the embodiment.

FIG. 11 is a graph showing a drop test result of a tuning fork-typevibrator according to a comparative example.

FIG. 12 is a drawing that illustrates a state of the tuning fork-typevibrator being held and pressurized between a break-off tool and thesuctioning tool used for mounting.

FIG. 13 is a drawing that illustrates the outer shape of a tuningfork-type vibration piece according to another embodiment of the presentinvention.

FIG. 14 is a drawing that illustrates the outer shape of a tuningfork-type vibration piece according to yet another embodiment of thepresent invention.

FIG. 15 is a drawing that illustrates the outer shape of a tuningfork-type vibration piece according to yet another embodiment of thepresent invention.

EMBODIMENTS OF THE INVENTION

Embodiments of the present invention are hereinafter described in detailreferring to the accompanying drawings.

FIG. 1 is a schematic view in cross section of a tuning fork-typecrystal vibrator (hereinafter referred to as “crystal vibrator”)according to an embodiment of the present invention. FIG. 2 is a planview of the crystal vibrator illustrated in FIG. 1 from which a lidmember 5 has been detached. FIG. 3 is an enlarged view of a main-surfaceside of a tuning fork-type crystal vibration piece (hereinafter referredto as “crystal vibration piece”). FIG. 4 is an enlarged view of anothermain-surface side of the crystal vibration piece 3.

In a crystal vibrator 1 according to this embodiment, the crystalvibration piece 3 is housed in a package 2 made of, for example, aceramic material. The package 2 includes a base 4 which is a body and alid member 5. The base 4 and the lid member 5 are joined to each otherwith a sealing member 6. Specifically, the crystal vibration piece 3 isjoined, with a pair of metal bumps 8; joining material, to a pair ofelectrode pads 7 on the base 4 having an opening on its upper side, andthe plate-shaped lid member is joined to the base 4 so as to close theopening. The joining material is not necessarily limited to the metalbumps 8 and may be selected from other materials including a conductiveresin adhesive and a brazing filler material.

While the nominal frequency of this crystal vibrator 1 according to thisembodiment is 32.768 kHz, other frequencies may be applicable instead ofthe nominal frequency.

The base 4 of the package 2 is a container having insulating propertieswhich is made of, for example, a ceramic or glass material. In thisembodiment, a ceramic material is used to make the base 4, and the base4 is formed by firing. The base 4 has an opening on its upper side andhas a recessed shape in cross section surrounded by a peripheral wall 4a. Inside of the base 4 (housing portion) is formed a step 4 b toreceive the crystal vibration piece 3. The step 4 b has, on its uppersurface, the electrode pads 7 that are formed in a pair. The electrodepads 7 are electrically connected to two terminal electrodes 9 on anouter bottom surface (back surface) of the base 4 through a wiringpattern, not illustrated in the drawing, formed inside of the base 4.

The lid member 5 is a solid plate rectangular in plan view and made of,for example, a metal, ceramic, or glass material.

The crystal vibrator 1 according to this embodiment is amicrominiaturized vibrator in which outer dimensions of the package 2rectangular in plan view are, for example, 1.6 mm×1.0 mm, and the heightof the package 2 inclusive of the lid member 5 is, for example, 0.45 mm.

The outer dimensions of the crystal vibrator 1 provided by the presentinvention are not thus limited and may be greater or smaller than thebefore-mentioned values, for example, 2.0 mm×1.2 mm or 1.2 mm×1.0 mm.

The crystal vibration piece 3 which will be housed in the package 2 ofthe crystal vibrator 1 are obtained from a sheet of crystal wafer notillustrated in the drawings. The outer shapes of multiple crystalvibration pieces 3 are formed on the crystal wafer at once byphotolithography, specifically, by, for example, wet etching using aresist or metal film as mask.

As illustrated in FIGS. 3 and 4 , the crystal vibration piece 3 includesa stem portion 10, a pair of first and second arm portions 11 and 12which are vibrating portions extending in parallel from one end side ofthe stem portion 10, and a joining portion 13 which is formed on theother end side of the stem portion 10 to join to the base 4.

The first and second arm portions 11 and 12 respectively have tip-sideparts 11 a and 12 a that are increased in width, i.e., increased indimension in a direction orthogonal to a direction in which the armportions 11 and 12 are extending (lateral direction on FIGS. 3 and 4 ).

Further, the first and second arm portions 11 and 12 respectively havegrooves 14 on their main surfaces illustrated in FIGS. 3 and 4 . Thegrooves 14 are formed along the extending direction of the arm portions11 and 12.

The crystal vibration piece 3 includes two first driving electrodes 15and second driving electrodes 16, and extraction electrodes 17 and 18that are respectively extracted from the driving electrodes 15 and 16 toelectrically connect these driving electrodes to the electrode pads 7 ofthe base 4. The first and second driving electrodes 15 and 16 are partlylocated in the grooves 14 formed on the two main surfaces.

The first driving electrodes 15 are respectively formed on both mainsurfaces of the first arm portion 11 inclusive of the grooves 14 and onboth side surfaces of the second arm portion 12. The first drivingelectrodes 15 are both connected to the extraction electrode 17.Similarly, the second driving electrodes 16 are respectively formed onboth main surfaces of the second arm portion 12 inclusive of the grooves14 and on both side surfaces of the first arm portion 11, and the seconddriving electrodes 16 are both connected to the extraction electrode 18.

Through holes 21 and 22 are formed in a pair in a region of the stemportion 10 where the driving electrodes 15 and 15 are formed. Thedriving electrodes 15 and 16 on the main surfaces are respectivelyinterconnected through the through holes 21 and 22. In this description,the through hole refers to a hole penetrating through the stem portionand having an inner wall surface coated with a metal film, serving as anelectrode. Instead of the through hole, the driving electrodes on themain surfaces in the crystal vibration piece may be respectivelyinterconnected through side surfaces of the stem portion or through aregion between joints of the arm and stem portions (origin ofbifurcation).

In the first and second arm portions 11 and 12, tip-of-arm electrodes 25and 24 are formed in regions increased in width of the tip-side parts 11a and 12 a along their circumferences. The tip-of-arm electrodes 24 and25 may have a thickness of, for example, approximately 0.1 μm to 0.4 μm.The tip-of-arm electrodes 25 formed along the circumference of thetip-side part 11 a are connected to the second driving electrodes 16formed on the side surfaces of the first arm portion 11. The tip-of-armelectrodes 24 formed along the circumference of the tip-side part 12 aare connected to the first driving electrodes 15 formed on the sidesurfaces of the second arm portion 12.

Frequency adjustment metal films 19 and 20 are formed on the tip-of-armelectrodes 25 and 24 on the main surfaces on one side illustrated inFIG. 3 . The frequency adjustment metal films 19, 20 are formed in aslightly smaller area than the tip-of-arm electrode 25, 24 and areirradiated with, for ample, a laser beam and thereby reduced in mass forcoarse frequency adjustment of the crystal vibration piece 3.

The first and second driving electrodes 15 and 16, extraction electrodes17 and 18, and tip-of-arm electrodes 24 and 25 of the crystal vibrationpiece 3 are thin films in which a metal, for example, gold, is depositedon chromium layers formed by metallization on the arm portions 11 and12. Such a thin film is formed on the whole surface of a base materialby, for example, vacuum deposition or sputtering and then subjected tometal etching using photolithography and formed into a desired shape.The metals used in the first and second driving electrodes 15 and 16,extraction electrodes 17 and 18, and tip-of-arm electrodes 24 and 25 arenot necessarily limited to the combination of chromium and gold, and mayinstead be the combination of chromium and silver.

The metal films 19 and 20 are formed on the tip-side parts 11 a and 12 aof the arm portions 11 and 12 by, for example, plating such aselectrolytic plating. The frequency adjustment metal films 19 and 20 maypreferably be formed in the process of forming the metal bumps 8described later. In this embodiment, gold (Au) is used to form thefrequency adjustment metal films 19 and 20.

The extraction electrode 17 extracted from the first driving electrodes15 is extended to and formed in a first joining portion 13 b on one endside of the joining portion 13. The extraction electrode 18 extractedfrom the second driving electrodes 16 is extended to and formed in asecond joining portion 13 a on the other end side.

Two metal bumps 8 are formed in the joining portion 13 on the othermain-surface side illustrated in FIG. 4 to be joined to the electrodepads 7 of the base 4. One of the metal bumps 8 is formed on theextraction electrode 17 in the first joining portion 13 b, while theother one of the metal bumps 8 is formed on the extraction electrode 18in the second joining portion 13 a. The metal bump 8 has an oval shapein plan view, however, may be shaped otherwise. Examples of the otheroptional shapes may include circular shapes, and polygonal, for example,rectangular and square shapes. The metal bumps 8 are formed by plating,for example, electrolytic plating.

A manufacturing method for a crystal vibrator according to thisembodiment includes a first step of forming the frequency adjustmentmetal films 19 and 22 by, for example, electrolytic plating on amain-surface side of the arm portions 11 and 12 in a respective one ofthe crystal vibration pieces 3 formed on a crystal wafer, and a secondstep of performing a coarse frequency adjustment by removing thefrequency adjustment metal films 19 and 22 in part for mass reductionthrough irradiation of a laser beam.

FIG. 5 is a drawing that illustrates the coarse frequency adjustmentthrough the laser beam irradiation. While FIG. 5 illustrates the laserbeam radiation toward the frequency adjustment metal film 19 formed onthe tip-side part 11 a of the first arm portion 11 alone, the coarsefrequency adjustment through the laser beam irradiation is alsoperformed for the frequency adjustment metal film 20 formed on thetip-side part 12 a of the second arm portion 12.

A laser beam source (not illustrated in the drawings) is positioned soas to face one main-surface side of the crystal vibration pieces 3 onthe crystal wafer. The laser beam is then radiated from the source so asto remove the frequency adjustment metal film 19 on the othermain-surface side.

This laser beam irradiation starts at the tip-side part (right side inFIG. 5 ) where the mass reduction induces a highest level of frequencyfluctuation, advancing along the width direction of the first armportion 11 (direction perpendicular to the drawing of FIG. 5 ) atpositions shifted by degrees toward the stem portion 10 of the first armportion 11 (left side on FIG. 5 ).

The radiated laser beam enters one main-surface side of the crystalvibration pieces 3 on the crystal wafer and transmits through crystal 26inside of the crystal vibration pieces 3, and then arrives at thefrequency adjustment metal films 19 formed on the opposite main-surfaceside, consequently removing the tip-of-arm electrodes 25 and thefrequency adjustment metal films 19 on the two main-surface sides.

By thus irradiating the frequency adjustment metal films 19 with thelaser beam directed from the upper side and transmitting through thecrystal 26 inside of the crystal vibration piece 3, metal fragmentschipped off the frequency adjustment metal films 19 may fly downwardaway from these metal films. This may prevent the metal fragments fromadhering again to the crystal vibration pieces 3. The laser beam may bedirected so as to transmit through the crystal from the lower to upperside of the crystal vibration pieces 3. The frequency adjustment metalfilm may be formed on the main surfaces on both sides of the crystalvibration piece.

The laser used in this embodiment is a green laser, however, may beselected from other lasers having different wavelengths, including YAGlaser.

As described earlier, frequencies of the multiple tuning fork-typevibration pieces on the crystal wafer may easily become more variable.In the microminiaturized crystal vibrator 1, therefore, the amount ofcoarse frequency adjustment with the frequency adjustment metal films 19and 20 under the laser beam irradiation may have to be increased toallow the variability to stay within a required range, which makes itnecessary to increase thicknesses of the frequency adjustment metalfilms 19 and 20. In such a microminiaturized crystal vibrator 1 asdescribed in this embodiment in which the package 2 has outer dimensionsof approximately 1.6 mm×1.0 mm, the frequency adjustment metal film 19,20 may preferably have a thickness of greater than or equal to 3 μm andless than or equal to more and 9 μm. The frequency adjustment metalfilms 19 and 20 in this embodiment are formed by plating as describedearlier, and are, for example 5 μm in thickness.

As the crystal vibrators are further miniaturized, the crystal vibrationpieces used in such vibrators are correspondingly smaller, narrowing anarea allowed for the frequency adjustment metal films to be formed. Ifthe frequency adjustment metal film is too large in area to ensure anenough amount of adjustment, the crystal vibrator may have poorproperties. Thus, securing a larger area of the frequency adjustmentmetal film alone does not necessarily promise a required level ofadjustment, which raises the need to increase the frequency adjustmentmetal films in thickness.

When the package of a crystal vibrator rectangular in plan view hasouter dimensions of 1.6 mm×1.0 mm as described in this embodiment, thefrequency adjustment metal films should necessarily be 3 μm or more inthickness.

In case the package rectangular in plan view is further reduced in sizeto, for example, outer dimensions of 1.2 mm×1.0 mm, the frequencyadjustment metal films may have to be 7 μm or more in thickness. In thatcase, the thickness of the frequency adjustment metal film may be atmost 13 μm or less in view of precisions required of frequencyadjustment and laser beam-used machining.

FIG. 6 is a drawing of a state after the frequency adjustment metal filmincreased in thickness is irradiated with a laser beam as illustrated inFIG. 5 .

Subsequent to the laser irradiation, one end thereby partly removed ofthe frequency adjustment metal 19 is roughened with a projection 27directed along the laser irradiation, as illustrated in FIG. 6 . FIG. 6is a drawing of the frequency adjustment metal film 19 on the tip-sidepart 11 a of the arm portion 11, similarly to FIG. 5 . The projection 27is also formed at one end of the frequency adjustment metal film 20 ofthe second arm portion 12 irradiated with the laser beam.

A height “h1” and a height “h” were measured with a laser microscope,where the “h1” is a height of the projection 27 from the surface of thefrequency adjustment metal film 19 at a position beyond the range oflaser irradiation on the outside of its one end partly removed, and the“h” is a height (thickness) from the raw surface of the crystal 26 tothe surface of the frequency adjustment metal film 19 at a positionbeyond the range of laser irradiation.

According to a result of this measurement, the height “h1” of theprojection 27 may be expressed by the following formula 1) using theheight (thickness) “h” from the raw surface of the crystal 26 to thesurface of the frequency adjustment metal film 19 at a position beyondthe range of laser irradiation.0.5h<h1≤1.2h  1)

The “h” is in the range of 3 μm≤h≤9 μm when the package 2 according tothis embodiment has outer dimensions of, for example, 1.6 mm×1.0 mm.

The “h” is in the range of 7 μm≤h≤13 μm when the package has smallerouter dimensions of 1.2 mm×1.0 mm than in this embodiment.

While the tip-of-arm electrode 25 in FIG. 6 , and FIG. 9 described lateris discernibly illustrated in a substantial thickness, the thickness ofthe tip-of-arm electrode 25 in life size is adequately small, ascompared with the “h”. Therefore, a total thickness, inclusive of thethickness of the tip-of-arm electrode 25, may be regarded as thethickness of the frequency adjustment metal film 19.

The projection 27 may easily chip off under an external impact, causingthe frequency fluctuations.

This embodiment, therefore, attempts to eliminate the projection 27formed by the laser beam irradiation at one end of the frequencyadjustment metal film 19, 20.

The multiple crystal vibration pieces 3 on the crystal wafer, subsequentto coarse frequency adjustment under the laser beam irradiation, arebroken off the crystal wafer into individual pieces, which are eachjoined to the electrode pads 7 and mounted in the package 2. The crystalvibrator manufacturing method according to this embodiment furtherincludes a third step of applying a load to and pressurizing portionsthe frequency adjustment metal films 19 and 20 with a suctioning toolused to suction the crystal vibration piece 3 when mounted on the base4. In this third step, the projection 27 on the roughened one end of thefrequency adjustment metal films 19 and 20 are pushed down under theapplied load.

How to push down the projection 27 during the mounting process ishereinafter described in detail.

The multiple crystal vibration pieces 3 have been roughly adjusted infrequency by the laser beam irradiation in the state of a crystal wafer.After that, the crystal vibration pieces 3 are each taken out from thecrystal wafer as individual pieces thereof with a break-off tool and aredelivered to a suction tool for mounting.

FIG. 7 is a drawing of the crystal vibration piece 3 being mounted onthe base 4 with a suctioning tool 23 used for this purpose. FIG. 8 is anenlarged view of the crystal vibration piece 3 and the suctioning tool23 in contact with each other. While FIGS. 7 and 8 illustrate thefrequency adjustment metal film 19 of the first arm portion 11 alone,the same goes for the frequency adjustment metal film 20 of the secondarm portion 12.

To mount the crystal vibration piece 3 on the base 4, the metal bumps 8of the extraction electrodes 17 and 18 on the main surfaces on one sideare ultrasonically joined by FCB (Flip Chip bonding) to the electrodepads 7 of the base 4. In the crystal vibration piece 3 illustrated inthese drawings, one main-surface side where no metal bump 8 is formed,i.e., one main-surface side where the frequency adjustment metal film 19is formed is directed upward, which is opposite to the illustrations ofFIGS. 5 and 6 .

The suctioning tool 23 according to this embodiment is so sized thatcovers a range of the crystal vibration piece 3, from the joiningportion 13 on one end side in the longitudinal direction (lateraldirection in FIGS. 7 and 8 ) where the metal bumps 18 are formed, to thetip-side parts on the other end side where the frequency adjustmentmetal films 19 and 20 are formed.

The suctioning tool 23 used for mounting may be selected from toolssuitable for the size of the package 2, i.e., the size of the crystalvibration piece 3 and is large enough to cover the crystal vibrationpiece 3 from its one end side to the other end side.

At the time of mounting the crystal vibration piece 3 on the base 4, thecrystal vibration piece 3 is suctioned and held by the suctioning tool23 and thereby located at a predefined mounting position on the base 4and then mounted on the base 4. Next, the crystal vibration piece 3 issubjected to a load and pressurized, and the electrode pads 7 of thebase 4 are then joined to the metal bumps 8 of the crystal vibrationpiece 3 under ultrasonic radiation while being heated at the same time.

The suctioning tool 23 subject to heat and ultrasonic radiation thenapplies a load to and pressurizes tip-side parts of the crystalvibration piece 3 where the frequency adjustment metal films 19 and 20are formed. After the crystal vibration piece 3 is mounted on the base4, the projection 27 on the roughened end of the frequency adjustmentmetal film 19 irradiated with the laser beam is pushed down into aprojection 27 a reduced in height, as illustrated in FIG. 9 .

When a load is applied to the crystal vibration piece 3 with thesuctioning tool 23, as illustrated in the enlarged view of FIG. 8 , asurface 23 a of the suctioning tool 23 on which the crystal vibrationpiece 3 is being held is pressed against the joining portion 13 on oneend side of the crystal vibration piece 3 where the metal bumps 8 areformed and the frequency adjustment metal film 19 on the other end side.On the other hand, an intermediate portion between one and the other endsides, i.e., a portion including the arm portions 11 and 12 andelectrodes at edges of the grooves 14 are slightly distanced from thereed-holding surface 23 a of the suctioning tool 23.

This may prevent that the arm portions 11 and 12 and electrodes at edgesof the grooves 14 accidentally contact the reed-holding surface 23 a ofthe suctioning tool 23 and are thereby damaged, avoiding possibleadverse effects on properties of the vibration piece 3.

In this embodiment, a soft metal that excels in malleability gold (Au),is used in the frequency adjustment metal film 19, 20. The projection 27formed on the frequency adjustment metal film 19, 20 made of thismaterial may be more easily pushed down toward the metal film. This mayallow the crystal vibration piece 3 to improve in stability.

As illustrated in FIG. 9 , a height “h2” and a height “h” were measuredwith a laser microscope, where the “h2” is a height of the projection 27a, which has been pushed down and reduced in height, from the surface ofthe frequency adjustment metal film 19 at a position beyond the range oflaser irradiation on the outside of its one end partly removed, and the“h” is a height (thickness) from the raw surface of the crystal 26 tothe surface of the frequency adjustment metal film 19 at a positionbeyond the range of laser irradiation.

These heights were measured similarly to the heights “h1” and “h” in theformula 1).

According to the obtained measurement result, the height “h2” of thepushed-down production 27 a reduced in height is expressed by thefollowing formula 2) using the height (thickness) “h” from the rawsurface of the crystal 26 to the surface of the frequency adjustmentmetal film 19 at a position beyond the range of laser irradiation.h2≤0.5h  2)

This may be rephrased that a thickness “h3” from the raw surface of thecrystal 26 to the surface of the frequency adjustment metal film 19 atone end partly removed of the frequency adjustment metal film 19 isgreater than the thickness “h” from the raw surface of the crystal 26 tothe surface of the frequency adjustment metal film at a position on theoutside of the one end partly removed of the frequency adjustment metalfilm 19, and a difference in height “h2” between the thickness “h3” atthe one end and the thickness “h” at a position on the outside of theone end is less than or equal to 0.5 times of the thickness “h”.

Similarly to the formula 1), the “h” in the formula 2) is in the rangeof 3 μm≤h≤9 μm when the package 2 has outer dimensions of 1.6 mm×1.0 mm,and is in the range of 7 μm≤h≤13 μm when the package 2 has outerdimensions of 1.2 mm×1.0 mm.

The formula 2) is not necessarily limited to the outer dimensions of 1.6mm×1.0 mm or 1.2 mm×1.0 mm but is also applicable to the outerdimensions of 2.0 mm×1.2 mm.

The thickness of the frequency adjustment metal film when the packagehas outer dimensions of 2.0 mm×1.2 mm may preferably be between 2 μm and5 μm.

At the time of mounting the crystal vibration piece 3 on the base 4, theprojection 27 at one end partly removed under the laser beam irradiationof the frequency adjustment metal film 19, 20 is pushed down by applyinga load using the suctioning tool 23. Provided that the “h” is a height(thickness) from the raw surface of the crystal 26 to the surface of thefrequency adjustment metal film 19, 20 at a position beyond the range oflaser irradiation, the projection 27 exceeding 0.5 h no longer exists,leaving the projection 27 a alone that has been pushed down and reducedin height. The projection 27 thus reduced in height may be unlikely tochip off under an external impact, which may suppress the risk offrequency fluctuations.

The crystal vibration piece 3 thus mounted on the base 4 with one sidebeing left open is irradiated with, for example, an ion beam for finalrefinement. Then, the lid member 5 is, for example, melted under heatand joined, with the sealing member 6, to the base 4 mounted with thecrystal vibration piece 3, and the crystal vibration piece 3 ishermetically sealed inside the package including the base 4 and the lidmember 5 to obtain the crystal vibrator 1. Examples of the hermeticsealing may include seal welding, beam welding, and atmospheric heating.

Next, a test result is hereinafter described that evaluated effects onimpact resistance exercised by the projection 27 formed at one end ofthe frequency adjustment metal film 19, 20 as a result of the time ofthe coarse frequency adjustment performed on the crystal wafer.

FIG. 10 is a drawing of a drop test result of the crystal vibrator 1manufactured by the method according to this embodiment.

FIG. 11 is a drawing of a drop test result of a crystal vibratoraccording to a comparative example in which the projection 27 formed asa result of the coarse frequency adjustment at the roughened one end ofthe frequency adjustment metal film 19, 20 is left uncrushed.

In the crystal vibrator according to this comparative example, adifferent suctioning tool was used, which was smaller in length than thesuctioning tool used for mounting in this embodiment in the extendingdirection of the first, second arm portion 11, 12 (lateral direction inFIGS. 7 and 8 ) of the crystal vibration piece 3 and thus not largeenough to apply a load to where the frequency adjustment metal film 19,20 was formed.

In the crystal vibrator according to the comparative example, therefore,the projection 27 formed at the roughened one end of the frequencyadjustment metal film 19, 20 is left uncrushed and sticking out.

FIGS. 10 and 11 show a measurement result, in which frequencyfluctuations were measured in five samples of the crystal vibrator 1according to this embodiment and five samples of the crystal vibratoraccording to the comparative example when they were dropped 10 timesfrom the height of 150 cm and when subsequently dropped again 10 timesfrom the height of 150 cm, and when they were dropped 10 times from theheight of 180 cm and when subsequently dropped again 10 times from theheight of 180 cm. In these drawings, their lateral axes representheights from which and how many times the crystal vibrators weredropped, and their longitudinal axes represent frequency deviationvalues, ΔF (ppm).

Frequency fluctuations were observed in none of the five samples of thecrystal vibrator 1 according to this embodiment in which the projection27 on the frequency adjustment metal film 19, 20 resulting from thecoarse frequency adjustment using the laser beam irradiation was pusheddown with the suctioning tool 23 when mounted on the base. On the otherhand, a large extent of frequency fluctuations—especially notableincreases to higher frequencies—was observed in the five samples of thecrystal vibrator according to the comparative example in which, whenmounted on the base, the suctioning tool failed to push down theprojection 27 on the frequency adjustment metal film 19, 20 resultingfrom the coarse frequency adjustment using the laser beam irradiation.

The samples of the crystal vibrator according to the comparative examplemarked notable increases to higher frequencies. These samples werechecked after their lid members 5 were detached from the bases 4, inwhich chipped-off fragments of the projections 27 formed on thefrequency adjustment metal films 19, 20 were found.

According to this embodiment, the projection 27 formed as a result ofthe frequency adjustment metal film 19, 20 being removed in part byirradiating the crystal vibration piece 3 with a beam is pushed downunder a load applied with the suctioning tool 23 when the vibrationpiece 3 is mounted on the base 4. This may prevent the unfavorable eventthat the projection 27 chips off under an external impact, suppressingthe risk of frequency fluctuations.

Another Embodiment

-   -   1) In the earlier embodiment, the projection 27 of the frequency        adjustment metal film 19, 20 is pushed down by applying a load        in the process of mounting the crystal vibration piece 3 on the        base 4. This action, however, is not necessarily included in        this process but may be performed at other times.

For example, the projection 27 of the frequency adjustment metal film19, 20 may be pushed down when each piece of the crystal vibrationpieces 3 broken off the crystal wafer with a break-off tool is receivedby the suctioning tool 23, specifically the projection 27 may be pusheddown while the frequency adjustment metal film 19, 20 is being heldbetween the break-off tool and the suctioning tool 23.

Specifically, a portion of the crystal vibration piece 3 where thefrequency adjustment metal films 19 and 20 are formed is held between abreak-off tool 28 and the suctioning tool 23, as illustrated in FIG. 12. Thus, the crystal vibration piece 3, when received by the suctioningtool 23, is held between the break-off tool 28 and the suctioning tool23 and subjected to a load to be pressurized, so that the projection 27of the frequency adjustment metal film 19, 20 is pushed down. In thisinstance, a recess 28 a is formed beforehand in the break-off tool 28 ata position corresponding to the metal bumps 8 so as to avoid any contactbetween a reed-holding surface of this tool from and the metal bumps 8.

The crystal vibration pieces 3 may be each broken off the crystal waferwith the break-off tool, with the projection 27 of the frequencyadjustment metal film 19, 20 being pushed down with this tool. Thus, theprojection 27 of the frequency adjustment metal film 19, 20 may beefficiently pushed down with the break-off tool when the crystalvibration pieces 3 are broken off into individual pieces.

Instead, the frequency adjustment metal films 19 and 20 in all of themultiple crystal vibration pieces 3 before they are broken off thecrystal wafer may be pressurized at once with an appropriate tool topush down any projections 27 formed in the vibration pieces 3.

In case the projection 27 of the frequency adjustment metal film 19, 20fails to be adequately pushed down under a load in one attempt, theprojection 27 may be pushed down in two stages; when each piece of thecrystal vibration pieces 3 is broken off the crystal wafer with thebreak-off tool, and when the crystal vibration piece 3 held with thebreak-off tool is received by the suctioning tool 23.

-   -   2) In the earlier embodiment, the joining portion 13        constituting part of the stem portion 10 extends in a direction        opposite to the extending direction of the first, second arm        portion 11, 12 and then in a direction orthogonal to the        extending direction (rightward in FIG. 3 ). The joining portion        13 may have a laterally symmetrical shape, lateral ends of which        extend in two directions included in the orthogonal direction        (leftward and rightward in FIG. 13 ), as is known from the outer        shape of the crystal vibration piece 3 illustrated in FIG. 13 .

As illustrated in FIG. 14 , the joining portion 13 may have a laterallysymmetrical shape, lateral ends of which extend in two directionsincluded in the orthogonal direction (leftward and rightward in FIG. 14) and further extend parallel to the extending direction of the first,second arm portion 11, 12.

As illustrated in FIG. 15 , the joining portion 13 may extend frombetween the first and second arm portions 11 and 12 in the extendingdirection of these arm portions. In the crystal vibration piece 3 inwhich the joining portion 13 is shaped as described so far, two metalbumps 8 to be joined to the electrode pads 7 of the base 4 are locatedat an end(s) of the extending joining portion 13, as illustrated inFIGS. 13 to 15 . The joining portion 13 may or may not have a portion(s)formed along the extending direction or a direction(s) orthogonal to theextending direction.

-   -   3) In the earlier embodiment, the metal bumps 8 are used to join        the crystal vibration piece 3 to the base 4, however, may be        replaced with any other suitable means but the bumps, for        example, a conductive adhesive. When such a means is used,        ultrasonic radiation for the crystal vibration piece 3 to be        joined to the base 4 may be unnecessary in which case a        suctioning tool simply designed to suction and hold the crystal        vibration piece 3 may be used to mount the vibration piece 3 on        the base 4.    -   4) The earlier embodiment uses the laser beam for frequency        adjustments, however, may use one selected from any suitable        beams but the laser beam, for example, ion beam.    -   5) In the earlier embodiment and modified examples described so        far, the present invention is applied to the crystal vibration        piece. The present invention, however, may also be applicable to        any other suitable piezoelectric materials but crystal.

REFERENCE SIGNS LIST

-   -   1 tuning fork-type crystal vibrator    -   2 package    -   3 tuning fork-type crystal vibration piece    -   4 base    -   5 lid member    -   7 electrode pad    -   8 metal bump    -   10 stem portion    -   11 first arm portion    -   12 second arm portion    -   13 joining portion    -   15 first driving electrode    -   16 second driving electrode    -   17, 18 extraction electrode    -   19, 20 frequency adjustment metal film    -   23 suctioning tool    -   24, 25 tip-of-arm electrode    -   26 crystal    -   27 projection (roughened end)    -   27 a projection (pressed down and reduced in height)

The invention claimed is:
 1. A tuning-fork type vibrator comprising: a package body having an opening; and a lid member sealing the opening of the package body, wherein the package body has a tuning-fork type vibrating piece and a housing in which the tuning-fork type vibrating piece is housed, the tuning-fork type vibrating piece includes a stem portion and a plurality of arm portions extending from the stem portion, the plurality of arm portions each having a frequency adjustment metal film that has been partly removed on a tip side part thereof, wherein, in the tuning-fork type vibrating piece, a first thickness from a raw surface of the tuning-fork type vibrating piece to a surface of the frequency adjustment metal film at the end of the tip side part is greater than a second thickness from the raw surface of the tuning-fork-type vibrating piece to the surface of the frequency adjustment metal film in a portion of the tip side part other than the end of the tip side part, and the difference between the first thickness and the second thickness is not greater than 0.5 times the second thickness; wherein the tuning-fork type vibrating piece is supported by being joined to an electrode of the housing of the package body, and wherein a package is formed in rectangular shape in plan view by joining the package body and the lid member, an outer dimension of the package is 1.6 mm×1.0 mm or less, and the frequency adjustment metal film has a thickness of 3 μm or more. 